When you select an invoice method different than 'No Invoice', all the parts lines except the 'Remove' ones and the fee lines will be invoiced. When you print a quotation, the price of parts and fees is shown only if you have an invoice method (you only have the quantity if you don't invoice) The invoice is available through a stat button. The price of removed parts is set to 0.0 by default as it won't be invoiced.